Experimental validation of single-sided bottom-hung window ventilation models

In Europe, single-sided natural ventilation through bottom-hung windows is widely used to improve indoor air quality and thermal comfort in buildings. Despite the existence of numerous empirical models to estimate its airflow rates, there is a lack of experimental model validation for this specific window opening design. This study evaluates the design characteristics and accuracy of existing empirical models for single-sided bottom-hung window ventilation by summarizing 12 models from publications, standards, and handbooks, analyzing their discrepancies, and assessing their performance based on experimental measurements. These models were compared in terms of considered factors, ventilation area definitions, and model sensitivity. The experimental validation involved 80 tracer gas measurements conducted over four months in a full-scale test bench under various weather conditions. Results revealed significant discrepancies in model performance, with most models underestimating airflow rates. Models specifically designed for bottom-hung windows demonstrated higher accuracy, whereas adapted models from simplified openings showed varied accuracy depending on the ventilation area definition. European and German standards consistently underestimated airflow rates, potentially leading to oversizing of window geometries and increased energy consumption. Conversely, the ASHRAE model significantly overestimated airflow rates due to its inappropriate wind-driven ventilation coefficient. Our study concludes that empirical models must be tailored to the specific characteristics of bottom-hung window configurations. Accurate modeling requires precise ventilation area definitions and incorporation of both buoyancy-driven and wind-driven ventilation mechanisms. Future research should focus on refining these models through in-situ calibration to enhance their applicability across diverse conditions.